In household refrigeration systems wherein air from within a compartment is recirculated over an evaporator, means are usually provided for periodically removing frost from the evaporator surfaces. In some instances, a defrost operation or cycle is initiated by actually detecting the presence of frost while, in other prior art system, a defrost operation is initiated at spaced predetermined time intervals. Typically, the defrost operation consists of deenergizing the system compressor and air circulating fan and the energization of heaters to melt the frost from the evaporator surfaces. The defrost operation may be terminated by sensing a temperature that indicates the absence of frost or in the alternative by allowing the defrost operation to continue for a period of time deemed sufficient to eliminate frost. The present invention relates to means for terminating defrost as soon as practical after the absence of frost is sensed.
In prior art defrost system bi-metal thermostats arranged on the evaporator have been employed to terminate defrost. This metal-to-metal contact with the evaporator allows accurate temperature sensing of the evaporator surfaces and is effective in terminating defrost. While this arrangement did, in fact, provide desirable results in terminating defrost and, more specifically, in deenergizing the heater, it did require careful installation to insure proper thermal contact between the bi-metal sensor and the evaporator surface. Further, since the thermostat is subjected to humidity and melting frost, it must be of the sealed type to prevent possible electrical shock hazards. The sealed type bi-metal thermostats for use in moist or substantially humid environments are expensive relative to the more open types used in environments wherein they do not come into contact with water or excessively humid conditions. Generally, bi-metal thermostats, when employed, are placed in direct thermal contact with a surface to minimize response time.
The present invention employs a bi-metal thermostat that is responsive to evaporator temperature, as sensed from a remote location.